The present invention relates to a device and a method for the coherent combination of optical beams or lasers separately amplified. The coherent combination of optical beams is a very promising technique for the development of high energy and/or high average power laser systems.
The constant tendency to develop lasers with higher and higher power and/or energy has to face different difficulties of realization. On the one hand, the power increase of a laser system generally induces a degradation of the beam quality, and on the other hand the extraction efficiency at high powers is limited by thermal effects occurring inside the amplifier materials.
A solution contemplated to obtain a high energy and/or high power beam is to use several sources or several independent amplifiers and to combine the beams coming from these different sources or these different amplifiers. This solution allows limiting the negative effects of thermal degradation induced for example in each of the amplifiers. However, for the combined beam to have the same optical qualities (spatial, spectral and temporal) as a single optical beam, it is not only required to spatially and temporally superimpose several optical beams, but the combination of the different beams has also to be coherent, i.e. the relative phase difference between the beams has to be null and stable over time. The condition of coherent superimposition is very difficult to achieve for optical beams because the phase difference has then to stay lower than a fraction of optical wavelength. Indeed, the relative phases of the different beams may fluctuate rapidly. The most difficult technical problem posed by the coherent recombination is to maintain a constant relative phase between different optical beams.
The coherent recombination of several optical beams has nevertheless been made by means of either passive or active devices.